Improved method for restoring petroleum hydrocarbon contaminated soil through resistance heating-chemical oxidation combined technology

Abstract

The invention provides a method for remedying petroleum hydrocarbon contaminated soil through an improved resistance heating-chemical oxidation combined technology, and relates to the field of petrochemical engineering environmental protection. The method comprises the following steps: S1, determining a polluted area; s2, doping a modifier and an oxidizing agent into the polluted area; s3, applying an alternating electric field to the polluted area to heat the soil; s4, volatile / semi-volatile organic pollutants escaping from the soil are treated after passing through an exhaust pipe, and high-boiling-point pollutants and an oxidizing agent are subjected to chemical action to be removed; the modifying agent comprises calcium oxide, the oxidizing agent comprises sodium persulfate, the mass of the sodium persulfate is 3-7% of the mass of the soil, the mass of the calcium oxide is 0.20-0.30% of the mass of the soil, and the electric field intensity is 1.75-3.25 V / cm. According to the method, the calcium oxide is doped to improve the resistance heating-oxidant coupling technology, the removal rate of the petroleum hydrocarbon reaches 78% within the test time of 2 h, and compared with the resistance heating-oxidant coupling technology under the same degradation rate, the energy consumption is reduced by about 20%, and the cost is saved by about 38%.

Description

Technical Field

[0001] The invention relates to the field of petrochemical environmental protection, and in particular to a method for repairing soil contaminated by petroleum hydrocarbons by using an improved resistance heating-chemical oxidation combined technology. Background Art

[0002] With the increase in the intensity of oil and gas exploration and development, the scale of natural gas production capacity continues to expand. However, in the process of natural gas field development, a large amount of oil-containing pollutants such as oily sludge and wastewater with various additives will be generated. The components of petroleum pollutants are complex and generally have the characteristics of strong hydrophobicity, low volatility, low solubility and strong adsorption. If not handled properly, they will enter the soil through runoff and infiltration, which will pose a great threat to the soil environment. Some scholars have shown through investigations on domestic petroleum hydrocarbon contaminated soil that different soil environments present different non-point source pollution problems. In recent years, the "Soil Pollution Prevention and Control Action Plan" and the "Soil Pollution Prevention and Control Law" have been successively introduced, which have put forward more stringent requirements for soil pollution prevention and control management, but the treatment and remediation of oil-contaminated soil is still in its infancy, and soil treatment is urgent.

[0003] At present, the remediation technologies that have been studied more include heat treatment, chemical oxidation, soil washing, biodegradation, etc. Heat treatment technology has attracted widespread attention in the remediation of organic contaminated soil due to its advantages such as flexible operation, stable operation, and high treatment efficiency. Among them, soil resistance heating technology (ERH) is a rapidly developing heat treatment technology with low energy consumption, high efficiency, and relatively simple construction. This technology is based on Ohm's law, converting electrical energy into thermal energy and increasing the soil temperature, that is, the electric field accelerates the transfer of kinetic energy of free charge carriers to cause energy conversion, and has now been used to remove organic pollutants in the soil. However, there are still certain limitations in the implementation of resistance heating technology, such as the maximum temperature does not exceed 120°C, high boiling point pollutants are difficult to remove, water evaporation loss is accelerated, and the single remediation time and cost are high.

[0004] Resistance heating technology is usually used in conjunction with other treatment technologies to solve the problems that exist in the process of using resistance heating alone. Among them, resistance heating-chemical oxidation is a synergistic remediation technology that has received a lot of attention. Chemical oxidation uses chemical oxidants to react with pollutants to degrade pollutants and reduce their toxicity. Compared with using resistance heating technology alone, coupling chemical oxidation with resistance heating can more effectively repair high-boiling-point pollutants. After coupling, the thermal field provided by resistance heating can not only thermally activate some oxidants, but also accelerate the sulfate free radicals (SO4 －·) and hydroxyl radicals (·OH), and can also heat the soil, enhancing the mass transfer rate and accessibility of pollutants. However, the implementation process is greatly affected by the electrode system parameter settings and the physical and chemical properties of the pollution, and the cost of the oxidant is high. It is urgent to carry out a large number of in-depth experimental studies to optimize the combined treatment effect.

[0005] The Chinese patent with publication number CN113305142A discloses a method for efficiently repairing soil petroleum hydrocarbon pollution. Calcium oxide reacts with water to generate calcium hydroxide, and the reaction process releases a large amount of heat. Therefore, calcium oxide activates sodium persulfate to provide complementary activation effects of alkali activation and thermal activation at the same time. Na2S2O8 first reacts with OH in the liquid phase. – The reaction generates OH 2 – and then with S2O8 2– The reaction results in the cleavage of the -OO- bond to produce SO4 – ·, under acidic and neutral conditions (pH = 2 ~ 7) to produce SO4 – · Mainly, and relatively stable in solution. In a solution with pH>8.5, SO4 – · then oxidized water or OH- gradually generates ·OH and the proportion increases, while in alkaline solution (pH>12) ·OH is mainly generated, because the oxidizing property of ·OH is higher than that of SO4 – Stronger, the degradation of the system also increases with the increase of alkalinity, high temperature provides enough activation energy to break the -OO- bond and lead to SO4 – The patent only infers theoretically that calcium oxide can enhance the oxidation of petroleum hydrocarbons by sodium persulfate. The examples do not provide specific data on the degradation rate of petroleum hydrocarbons after adopting this solution, nor is it known how the amount of calcium oxide added will affect the oxidation efficiency of sodium persulfate on petroleum hydrocarbons. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides an improved method for remediating petroleum hydrocarbon contaminated soil by using a resistance heating combined technology. The method adds calcium oxide, which reacts exothermically with water in the soil environment to strengthen thermal activation and generate calcium hydroxide with strong alkalinity. Sodium persulfate is activated and decomposed under heat and alkaline conditions to produce sulfate radicals (SO4 － ·) and hydroxyl radicals (·OH), which react with organic matter to destroy its structure.

[0007] The technical solution of the present invention is as follows:

[0008] The present invention provides a method for remediating petroleum hydrocarbon contaminated soil by using an improved resistance heating-chemical oxidation combined technology, comprising the following steps:

[0009] S1. Identify the contaminated area;

[0010] S2. Adding improvers and oxidants to the contaminated area;

[0011] S3. Apply an alternating electric field to the contaminated area to heat the soil;

[0012] S4. Volatile / semi-volatile organic pollutants escaping from the soil are treated after passing through the exhaust pipe, and high boiling point pollutants react chemically with oxidants and are removed;

[0013] The modifier includes calcium oxide, the oxidant includes sodium persulfate, the mass of the sodium persulfate is 3-7% of the mass of the soil, the mass of the calcium oxide is 0.20-0.30% of the mass of the soil, and the electric field strength is 1.75-3.25V / cm.

[0014] In a specific embodiment, the mass of sodium persulfate is 5% of the mass of the soil, the mass of calcium oxide is 0.25% of the mass of the soil, and the electric field strength is 2.5 V / cm.

[0015] In a specific embodiment, in step S2, sodium persulfate is first dissolved in water and then added.

[0016] In a specific embodiment, the moisture content of the soil is 30%-50%.

[0017] In a specific embodiment, in step S3, the soil is heated for 1-4 hours.

[0018] In a specific embodiment, in step S3, the soil is heated for 2 hours.

[0019] In a specific embodiment, in step S4, volatile / semi-volatile organic pollutants escaping from the soil enter the activated carbon absorption tube through the exhaust pipe and are adsorbed.

[0020] In a specific embodiment, step S1 further includes: removing plant residues, and then grinding and sieving.

[0021] In one embodiment, the sieve has a pore size of 0.425 mm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention improves the resistance heating-oxidant coupling technology by adding calcium oxide. The repaired soil meets the requirements of the petroleum hydrocarbon index in the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard" (Trial) (GB36600-2018), and the petroleum hydrocarbon removal rate reaches 78% within the 2h test time. Compared with the resistance heating-oxidant coupling technology under the same degradation rate, the energy consumption is reduced by about 20%, and the cost is saved by about 38%. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0025] The preparation of contaminated soil and the remediation test device in the examples and comparative examples are as follows:

[0026] 1. Preparation of petroleum-contaminated soil with a TPH mass fraction of about 5000 mg / kg: Uncontaminated soil was collected from farmland around Luojiang District, Deyang City. The soil surface sample of 5 to 20 cm was taken, and plant residues, stones and other debris were picked out. After air drying, grinding, sieving (0.425 mm pore size), and storing in the dark for later use; quantitatively weigh 20 g 0 # Diesel (density 0.84g / cm 3 , purchased from a gas station in Chengdu), dissolved in n-hexane, added to 4 kg of farmland soil, stirred while adding, then rinsed the beaker with n-hexane several times, added to the soil, stirred evenly and placed in a fume hood for 24 hours until the n-hexane evaporated completely, to obtain petroleum contaminated soil, and finally measured its total petroleum hydrocarbon mass fraction was 4635.25 mg / kg.

[0027] 2. Build a repair test device: It mainly includes a heating unit and an extraction unit. The heating unit consists of a crucible with a cover, an insulating layer, an exhaust hole, an electrode, and an AC power supply component. The extraction unit consists of an exhaust hole and activated carbon.

[0028] 3. Repair principle: Resistance heating will thermally activate sodium persulfate, breaking the OO bond in the persulfate molecule to form SO4 － ·, calcium oxide is added. Calcium oxide reacts exothermically with water in the soil environment, strengthening thermal activation and generating calcium hydroxide with strong alkalinity. Sodium persulfate is activated and decomposed into sulfate radicals (SO4 － ·) and hydroxyl radicals (·OH), which react with organic matter to destroy its structure. The specific reaction pathway is as follows:

[0029] S2O8 2- +heat→2SO4 - ·

[0030] CaO+H2O→Ca(OH)2

[0031] S2O8 2- →SO4 - +3SO4 2- +4H + +O2 -

[0032] SO4 - +OH - →SO4 2- + OH

[0033] 4. Petroleum hydrocarbon degradation effect test: According to the standard "Petroleum hydrocarbons in soil and sediments (C 10 -C 40 ) was used to determine the petroleum hydrocarbon content before and after repair.

[0034] Comparative Example 1

[0035] The contents of the reagents and materials required in this comparative example are as follows: 400 g of soil, 160 mL of deionized water, 20 g of sodium persulfate (5%), and an electric field strength of 2.5 V / cm.

[0036] The specific steps are as follows:

[0037] (1) First, pour 400 g of contaminated soil into a beaker, take 20 g of sodium persulfate and 160 mL of deionized water according to the experimental ratio, pour the sodium persulfate into the deionized water, and after the sodium persulfate is dissolved, add the soil and stir it evenly with a glass rod. Then pour it into a polytetrafluoroethylene crucible, insert the electrodes and connect the power supply. The voltage is set to 2.5 V / cm, and the soil is heated for 2 h. The exhaust gas enters the activated carbon absorption tube through the exhaust pipe and is adsorbed.

[0038] (2) Take 2 g of the soil sample after repair in step (1) and place it in a round-bottom centrifuge tube, add n-hexane to make up to 20 mL, and shake to mix well.

[0039] (3) After step (2), the centrifuge tube was placed in an ultrasonic instrument and ultrasonicated at 20°C for 15 min. The ultrasonicated centrifuge tube was placed in a high-speed centrifuge and centrifuged at 1000 r / min for 5 min. The supernatant was then poured into a round-bottom flask.

[0040] (4) Repeat step (3) three times until the supernatant is clear, and then use a rotary evaporator to evaporate the extract in the flat-bottom flask. The first time, evaporation is performed until 3-4 ml is left. The impurities in the extract are filtered out with a magnesium silicate column and the vegetable oil is adsorbed. Finally, the filtrate is evaporated to 1 ml and placed in a brown injection bottle, and the volume is adjusted to 1.5 mL with n-hexane. 1 μl of the sample is drawn with an injection needle and injected into the instrument. The petroleum hydrocarbon content is determined using the method of "Gas Chromatographic Method for Determination of Petroleum Hydrocarbons (C10-C40) in Soil and Sediment" (HJ 1021-2019).

[0041] After remediation, the petroleum hydrocarbon content in the soil was 1272.74 mg / kg, and the degradation rate was 72.54%, which met the index requirements of the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard" (Trial) (GB36600-2018); the sodium persulfate residual rate was 58%, the energy consumption required for the 2h test process was 0.02437 kW·h, and the reagent cost was 0.128 yuan.

[0042] Example 1

[0043] The contents of the reagents and materials required in this example are as follows: 400 g of soil, 160 mL of deionized water, 20 g of sodium persulfate (5%), 1 g of calcium oxide (0.25%), and an electric field strength of 2.5 V / cm.

[0044] The specific steps are as follows:

[0045] (1) First, pour 400g of contaminated soil into a beaker, and according to the experimental ratio, take 1g of calcium oxide and 20g of sodium persulfate, mix the calcium oxide with dry soil, pour the sodium persulfate into 160mL of deionized water, wait for the sodium persulfate to dissolve, add the soil and stir evenly with a glass rod, then pour it into a polytetrafluoroethylene crucible, insert the electrodes and connect the power supply, set the voltage to 2.5V / cm, heat the soil for 2h, and let the exhaust gas enter the activated carbon absorption tube through the exhaust pipe and be adsorbed.

[0046] (2) Take 2 g of the soil sample after repair in step (1) and place it in a round-bottom centrifuge tube, add n-hexane to make up to 20 mL, and shake to mix well.

[0047] (3) After step (2), the centrifuge tube was placed in an ultrasonic instrument and ultrasonicated at 20°C for 15 min. The ultrasonicated centrifuge tube was then placed in a high-speed centrifuge and centrifuged at 1000 r / min for 5 min. The supernatant was poured into a round-bottom flask.

[0048] (4) Repeat step (3) three times until the supernatant is clear, and then use a rotary evaporator to evaporate the extract in the flat-bottom flask. The first time, evaporation is performed until 3-4 ml is left. The impurities in the extract are filtered out using a magnesium silicate column and the vegetable oil is adsorbed. Finally, the filtrate is evaporated to 1 ml and placed in a brown injection bottle. The volume is adjusted to 1.5 ml with n-hexane. 1 μl of the sample is drawn with an injection needle and injected into the instrument. The petroleum hydrocarbon content is determined using the method of "Gas Chromatographic Method for Determination of Petroleum Hydrocarbons (C10-C40) in Soil and Sediment" (HJ 1021-2019).

[0049] After remediation, the petroleum hydrocarbon content in the soil was 1027.81 mg / kg, and the degradation rate was 77.83%, which met the index requirements of the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard" (Trial) (GB36600-2018); the sodium persulfate residual rate was 16.6%, and the energy consumption required for the 2h test process was 0.02849 kW·h, which was 16.91% higher than that of comparative example 1, and the reagent cost was 0.1290 yuan, which was 0.77% higher than that of comparative example 1.

[0050] Comparative Example 2

[0051] The contents of the reagents and materials required in this comparative example are as follows: 400 g of soil, 160 mL of deionized water, 28 g of sodium persulfate (7%), and an electric field strength of 2.5 V / cm.

[0052] The specific steps are as follows:

[0053] (1) First, pour 400 g of contaminated soil into a beaker, take 28 g of sodium persulfate and 160 mL of deionized water according to the experimental ratio, pour the sodium persulfate into the deionized water, and after the sodium persulfate is dissolved, add the soil and stir it evenly with a glass rod. Then pour it into a polytetrafluoroethylene crucible, insert the electrodes and connect the power supply. The voltage is set to 2.5 V / cm, and the soil is heated for 2 h. The exhaust gas enters the activated carbon absorption tube through the exhaust pipe and is adsorbed.

[0054] (2) Take 2 g of the soil sample after repair in step (1) and place it in a round-bottom centrifuge tube, add n-hexane to make up to 20 mL, and shake to mix well.

[0055] (3) After step (2), the centrifuge tube was placed in an ultrasonic instrument and ultrasonicated at 20°C for 15 min. The ultrasonicated centrifuge tube was then placed in a high-speed centrifuge and centrifuged at 1000 r / min for 5 min. The supernatant was poured into a round-bottom flask.

[0056] (4) Repeat step (3) three times until the supernatant is clear, and use a rotary evaporator to evaporate the extract in the flat-bottom flask. The first time, evaporation is performed until 3-4 ml is left. The impurities in the extract are filtered out using a magnesium silicate column and the vegetable oil is adsorbed. Finally, the filtrate is evaporated to 1 ml and placed in a brown injection bottle. The volume is adjusted to 1.5 ml with n-hexane. 1 μl of the sample is drawn with an injection needle and injected into the instrument. The petroleum hydrocarbon content is determined using the method of "Gas Chromatographic Method for Determination of Petroleum Hydrocarbons (C10-C40) in Soil and Sediment" (HJ 1021-2019).

[0057] After remediation, the petroleum hydrocarbon content in the soil was 977.44 mg / kg, and the degradation rate was 78.91%, which met the index requirements of the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard" (Trial) (GB36600-2018); the sodium persulfate residual rate was 5%, and the energy consumption required for the 2h test process was 0.03381 kW·h, which was 38.74% higher than that of comparative example 1, and the reagent cost was 0.1792 yuan, which was 40% higher than that of comparative example 1.

[0058] Comparative Example 3

[0059] The contents of the reagents and materials required in this comparative example are as follows: 400 g of soil, 160 mL of deionized water, 20 g of sodium persulfate (5%), 2 g of calcium oxide (0.5%), and an electric field strength of 2.5 V / cm.

[0060] The specific steps are as follows:

[0061] (1) First, pour 400g of contaminated soil into a beaker, and take 2g of calcium oxide and 20g of sodium persulfate according to the experimental ratio. Mix the calcium oxide with the dry soil, pour the sodium persulfate into 160mL of deionized water, and after the sodium persulfate is dissolved, add the soil and stir evenly with a glass rod. Then pour it into a polytetrafluoroethylene crucible, insert the electrodes and connect the power supply. The voltage is set to 2.5V / cm, and the soil is heated for 2h. The exhaust gas enters the activated carbon absorption tube through the exhaust pipe and is adsorbed.

[0062] (2) Take 2 g of the soil sample after repair in step (1) and place it in a round-bottom centrifuge tube, add n-hexane to make up to 20 mL, and shake to mix well.

[0063] (3) After step (2), the centrifuge tube was placed in an ultrasonic instrument and ultrasonicated at 20°C for 15 min. The ultrasonicated centrifuge tube was then placed in a high-speed centrifuge and centrifuged at 1000 r / min for 5 min. The supernatant was poured into a round-bottom flask.

[0064] (4) Repeat step (3) three times until the supernatant is clear, and then use a rotary evaporator to evaporate the extract in the flat-bottom flask. The first time, evaporation is performed until 3-4 ml is left. The impurities in the extract are filtered out using a magnesium silicate column and the vegetable oil is adsorbed. Finally, the filtrate is evaporated to 1 ml and placed in a brown injection bottle. The volume is adjusted to 1.5 ml with n-hexane. 1 μl of the sample is drawn with an injection needle and injected into the instrument. The petroleum hydrocarbon content is determined using the method of "Gas Chromatographic Method for Determination of Petroleum Hydrocarbons (C10-C40) in Soil and Sediment" (HJ 1021-2019).

[0065] After remediation, the petroleum hydrocarbon content in the soil was 2045.87 mg / kg, and the degradation rate was 55.86%, which met the index requirements of the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard" (Trial) (GB36600-2018); the sodium persulfate residual rate was 31.6%, and the energy consumption required for the 2h test process was 0.02868 kW·h, which was 10.69% higher than that of comparative example 1, and the reagent cost was 0.1300 yuan, which was 1.54% higher than that of comparative example 1.

[0066] Comparative Example 4

[0067] The contents of the reagents and materials required in this comparative example are as follows: 400 g of soil, 160 mL of deionized water, 20 g of sodium persulfate (5%), 4 g of calcium oxide (1%), and an electric field strength of 2.5 V / cm.

[0068] The specific steps are as follows:

[0069] (1) First, pour 400g of contaminated soil into a beaker, and take 4g of calcium oxide and 20g of sodium persulfate according to the experimental ratio. Mix the calcium oxide and dry soil, and pour the sodium persulfate into 160mL of deionized water. After the sodium persulfate is dissolved, add the soil and stir it evenly with a glass rod. Then pour it into a polytetrafluoroethylene crucible, insert the electrodes and connect the power supply. The voltage is set to 2.5V / cm, and the soil is heated for 2h. The exhaust gas enters the activated carbon absorption tube through the exhaust pipe and is adsorbed.

[0070] (2) Take 2 g of the soil sample after repair in step (1) and place it in a round-bottom centrifuge tube, add n-hexane to make up to 20 mL, and shake to mix well.

[0071] (3) After step (2), the centrifuge tube was placed in an ultrasonic instrument and ultrasonicated at 20°C for 15 min. The ultrasonicated centrifuge tube was then placed in a high-speed centrifuge and centrifuged at 1000 r / min for 5 min. The supernatant was poured into a round-bottom flask.

[0072] (4) Repeat step (3) three times until the supernatant is clear, and then use a rotary evaporator to evaporate the extract in the flat-bottom flask. The first time, evaporation is performed until 3-4 ml is left. The impurities in the extract are filtered out using a magnesium silicate column and the vegetable oil is adsorbed. Finally, the filtrate is evaporated to 1 ml and placed in a brown injection bottle. The volume is adjusted to 1.5 ml with n-hexane. 1 μl of the sample is drawn with an injection needle and injected into the instrument. The petroleum hydrocarbon content is determined using the method of "Gas Chromatographic Method for Determination of Petroleum Hydrocarbons (C10-C40) in Soil and Sediment" (HJ 1021-2019).

[0073] After remediation, the petroleum hydrocarbon content in the soil was 2027.11 mg / kg, and the degradation rate was 56.27%, which met the index requirements of the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard" (Trial) (GB36600-2018); the sodium persulfate residual rate was 16.6%, and the energy consumption required for the 2h test process was 0.024015 kW·h, which was 7.3% lower than that of comparative example 1. The reagent cost was 0.1320 yuan, which was 3.09% higher than that of comparative example 1.

[0074] Comparative Example 5

[0075] The contents of the reagents and materials required in this comparative example are as follows: 400 g of soil, 160 mL of deionized water, 20 g of sodium persulfate (5%), 8 g of calcium oxide (2%), and an electric field strength of 2.5 V / cm.

[0076] The specific steps are as follows:

[0077] (1) First, pour 400g of contaminated soil into a beaker, and take 8g of calcium oxide and 20g of sodium persulfate according to the experimental ratio. Mix the calcium oxide and dry soil, pour the sodium persulfate into 160mL of deionized water, and after the sodium persulfate is dissolved, add the soil and stir it evenly with a glass rod. Then pour it into a polytetrafluoroethylene crucible, insert the electrodes and connect the power supply. The voltage is set to 2.5V / cm, and the soil is heated for 2h. The exhaust gas enters the activated carbon absorption tube through the exhaust pipe and is adsorbed.

[0078] (2) Take 2 g of the soil sample after repair in step (1) and place it in a round-bottom centrifuge tube, add n-hexane to make up to 20 mL, and shake to mix well.

[0079] (3) After step (2), the centrifuge tube was placed in an ultrasonic instrument and ultrasonicated at 20°C for 15 min. The ultrasonicated centrifuge tube was then placed in a high-speed centrifuge and centrifuged at 1000 r / min for 5 min. The supernatant was poured into a round-bottom flask.

[0080] (4) Repeat step (3) three times until the supernatant is clear, and then use a rotary evaporator to evaporate the extract in the flat-bottom flask. The first time, evaporation is performed until 3-4 ml is left. The impurities in the extract are filtered out using a magnesium silicate column and the vegetable oil is adsorbed. Finally, the filtrate is evaporated to 1 ml and placed in a brown injection bottle. The volume is adjusted to 1.5 ml with n-hexane. 1 μl of the sample is drawn with an injection needle and injected into the instrument. The petroleum hydrocarbon content is determined using the method of "Gas Chromatographic Method for Determination of Petroleum Hydrocarbons (C10-C40) in Soil and Sediment" (HJ 1021-2019).

[0081] After remediation, the petroleum hydrocarbon content in the soil was 1287.31 mg / kg, and the degradation rate was 72.23%, which met the index requirements of the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard" (Trial) (GB36600-2018); the sodium persulfate residual rate was 19.9%, and the energy consumption required for the 2h test process was 0.02591 kW·h, which was 6.32% higher than that of comparative example 1, and the reagent cost was 0.135904 yuan, which was 6.18% higher than that of comparative example 1.

[0082] Comparative Example 6

[0083] The contents of the reagents and materials required in this comparative example are as follows: 400 g of soil, 160 mL of deionized water, 20 g of sodium persulfate (5%), 12 g of calcium oxide (3%), and an electric field strength of 2.5 V / cm.

[0084] The specific steps are as follows:

[0085] (1) First, pour 400g of contaminated soil into a beaker, and according to the experimental ratio, take 12g of calcium oxide and 20g of sodium persulfate, mix the calcium oxide with dry soil, pour the sodium persulfate into 160mL of deionized water, wait for the sodium persulfate to dissolve, add the soil and stir evenly with a glass rod, then pour it into a polytetrafluoroethylene crucible, insert the electrodes and connect the power supply, set the voltage to 2.5V / cm, heat the soil for 2h, and let the exhaust gas enter the activated carbon absorption tube through the exhaust pipe and be adsorbed.

[0086] (2) Take 2 g of the soil sample after repair in step (1) and place it in a round-bottom centrifuge tube, add n-hexane to make up to 20 mL, and shake to mix well.

[0087] (3) After step (2), the centrifuge tube was placed in an ultrasonic instrument and ultrasonicated at 20°C for 15 min. The ultrasonicated centrifuge tube was then placed in a high-speed centrifuge and centrifuged at 1000 r / min for 5 min. The supernatant was poured into a round-bottom flask.

[0088] (4) Repeat step (3) three times until the supernatant is clear, and then use a rotary evaporator to evaporate the extract in the flat-bottom flask. The first time, evaporation is performed until 3-4 ml is left. The impurities in the extract are filtered out using a magnesium silicate column and the vegetable oil is adsorbed. Finally, the filtrate is evaporated to 1 ml and placed in a brown injection bottle. The volume is adjusted to 1.5 ml with n-hexane. 1 μl of the sample is drawn with an injection needle and injected into the instrument. The petroleum hydrocarbon content is determined using the method of "Gas Chromatographic Method for Determination of Petroleum Hydrocarbons (C10-C40) in Soil and Sediment" (HJ 1021-2019).

[0089] After remediation, the petroleum hydrocarbon content in the soil was 1502.23 mg / kg, and the degradation rate was 67.59%, which met the index requirements of the "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard" (Trial) (GB36600-2018); the sodium persulfate residual rate was 0%, and the energy consumption required for the 2h test process was 0.03157 kW·h, which was 21.84% higher than that of comparative example 1, and the reagent cost was 0.1399 yuan, which was 9.26% higher than that of comparative example 1.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for remediating petroleum hydrocarbon contaminated soil using an improved resistance heating-chemical oxidation combined technology, characterized in that: The steps include: S1. Identify the contaminated area; S2. Adding improvers and oxidants to the contaminated area; S3. Apply an alternating electric field to the contaminated area to heat the soil; S4. Volatile / semi-volatile organic pollutants escaping from the soil are treated after passing through the exhaust pipe, and high boiling point pollutants react chemically with oxidants and are removed; The modifier includes calcium oxide, the oxidant includes sodium persulfate, the mass of the sodium persulfate is 3-7% of the mass of the soil, the mass of the calcium oxide is 0.20-0.30% of the mass of the soil, and the electric field strength is 1.75-3.25V / cm.

2. The method for remediating petroleum hydrocarbon contaminated soil by using the improved resistance heating-chemical oxidation combined technology according to claim 1 is characterized in that: The mass of sodium persulfate is 5% of the mass of the soil, the mass of calcium oxide is 0.25% of the mass of the soil, and the electric field strength is 2.5 V / cm.

3. The method for remediating petroleum hydrocarbon contaminated soil by using the improved resistance heating-chemical oxidation combined technology according to claim 1 is characterized in that: In step S2, sodium persulfate is first dissolved in water and then added.

4. The method for remediating petroleum hydrocarbon contaminated soil by using the improved resistance heating-chemical oxidation combined technology according to claim 1 is characterized in that: The moisture content of the soil is between 30% and 50%.

5. The method for remediating petroleum hydrocarbon contaminated soil by using the improved resistance heating-chemical oxidation combined technology according to claim 1, characterized in that: In step S3, the soil is heated for 1-4 hours.

6. The method for remediating petroleum hydrocarbon contaminated soil by using the improved resistance heating-chemical oxidation combined technology according to claim 1 is characterized in that: In step S3, the soil is heated for 2 hours.

7. The method for remediating petroleum hydrocarbon contaminated soil by using the improved resistance heating-chemical oxidation combined technology according to claim 1, characterized in that: In step S4, the volatile / semi-volatile organic pollutants escaping from the soil enter the activated carbon absorption tube through the exhaust pipe and are adsorbed.

8. The method for remediating petroleum hydrocarbon contaminated soil by using the improved resistance heating-chemical oxidation combined technology according to claim 1 is characterized in that: Step S1 also includes: removing plant residues, and then grinding and sieving.

9. The method for remediating petroleum hydrocarbon contaminated soil by using the improved resistance heating-chemical oxidation combined technology according to claim 8, characterized in that: The sieve aperture is 0.425 mm.